I had installed 3/4" plywood over the sub-floor and when the installer came to install the ceramic tiles, he said that there was too much bounce to the floor and he checked under the crawl space and discovered that the joist are not supported correctly. He advised me not to do anything until this was corrected. The house is only 2 years old and he told me to check with the township building code office.
Answer:
Who built the house? How long ago? If you're in an area where there's a local home builders' association, they will have to be your first phone call. This is just the beginning but they'll be able to guide you all the way.
